const singleComment = Symbol('singleComment')
const multiComment = Symbol('multiComment')

const stripWithoutWhitespace = () => ''
const stripWithWhitespace = (string, start, end) => string.slice(start, end).replace(/\S/g, ' ')

const isEscaped = (jsonString, quotePosition) => {
  let index = quotePosition - 1
  let backslashCount = 0

  while (jsonString[index] === '\\') {
    index -= 1
    backslashCount += 1
  }

  return Boolean(backslashCount % 2)
}

export default function stripJsonComments(jsonString, { whitespace = true } = {}) {
  if (typeof jsonString !== 'string') {
    throw new TypeError(`Expected argument \`jsonString\` to be a \`string\`, got \`${typeof jsonString}\``)
  }

  const strip = whitespace ? stripWithWhitespace : stripWithoutWhitespace

  let isInsideString = false
  let isInsideComment = false
  let offset = 0
  let result = ''

  for (let index = 0; index < jsonString.length; index++) {
    const currentCharacter = jsonString[index]
    const nextCharacter = jsonString[index + 1]

    if (!isInsideComment && currentCharacter === '"') {
      const escaped = isEscaped(jsonString, index)
      if (!escaped) {
        isInsideString = !isInsideString
      }
    }

    if (isInsideString) {
      continue
    }

    if (!isInsideComment && currentCharacter + nextCharacter === '//') {
      result += jsonString.slice(offset, index)
      offset = index
      isInsideComment = singleComment
      index++
    } else if (isInsideComment === singleComment && currentCharacter + nextCharacter === '\r\n') {
      index++
      isInsideComment = false
      result += strip(jsonString, offset, index)
      offset = index
      continue
    } else if (isInsideComment === singleComment && currentCharacter === '\n') {
      isInsideComment = false
      result += strip(jsonString, offset, index)
      offset = index
    } else if (!isInsideComment && currentCharacter + nextCharacter === '/*') {
      result += jsonString.slice(offset, index)
      offset = index
      isInsideComment = multiComment
      index++
      continue
    } else if (isInsideComment === multiComment && currentCharacter + nextCharacter === '*/') {
      index++
      isInsideComment = false
      result += strip(jsonString, offset, index + 1)
      offset = index + 1
      continue
    }
  }

  return result + (isInsideComment ? strip(jsonString.slice(offset)) : jsonString.slice(offset))
}
